1. Field of the Invention
The present invention relates to methods of producing thin-walled resilient sensitive elements, and particularly to methods of producing bellows from metal alloys.
Most advantageously the invention may be used in instrument manufacture.
2. Description of the Prior Art
Though the methods of making bellows on an industrial scale have been mastered long ago, the amount of defective products obtained when using these methods is still as high as 40 to 70% of the total amount of the manufactured products.
It is well known that bellows, being sensitive elements of many various devices, should retain their properties (rigidity, sealing, proportionality between the elastic deformation and the load applied) in a wide range of temperatures and pressures under prolonged static and dynamic loads in various weather conditions and in various agressive media. It is due to the above that bellows should meet rather rigid requirements. The quality of a bellow depends mainly on production techniques and on the properties of the metal alloy used for making it. Many attempts have been made to improve the production procedure for making bellows but all of them failed to considerably reduce the above percentage of defective products.
Known in the art is a method of producing bellows from a plurality of shaped annular diaphragms (see Burtsev K.N., Metallicheskie silfony, "Mashgiz", Moskva, Leningrad, 1963, pp. 6, 7, 80-82). According to this method, the annular diaphragms are welded together along the inner and outer edges thereof.
Though this method is in general use and the welding conditions are worked out to a rather high degree, the great amount of joint welds makes checking the manufactured product very difficult and in most cases is responsible for a loss of sealing.
There is also known in the art a method of producing bellows from metal alloys without welding (see Burtsev K.N., Metallicheskie silfony, "Mashgiz", Moskva, Leningrad, 1963, pp. 83-125). According to this method, a tubular workpiece is reeled to reduce the wall thickness thereof under volume deformation. The reeled tubular workpiece is heated up to a temperature exceeding that of recrystallization of the alloy. The heating process is carried out in a muffle furnace at a rate of 10.degree. to 20.degree. C. per sec. The thus heated tubular workpiece is cooled down in water. The tubular workpiece wall is locally deformed in a transverse direction to form annular grooves therein. Then the inner space of the tubular workpiece is filled with a fluid, and excessive pressure is produced within said inner space. The workpiece is compressed on axial direction, which causes plastic deformation of its wall, and thus corrugations are made. The corrugated workpiece is heated to a temperature at which finely dispersed phases of the alloy precipitate at a maximum rate. The heating process is carried out in a vacuum furnace at a rate of 1.degree. to 1.5.degree. C. per sec, the workpiece being held in a special clamping device which allows the same workpiece to acquire predetermined sizes. At the above temperature at which finely dispersed phases of the alloy precipitate at a maximum rate, the corrugated workpiece is held for 4 to 5 hours. The bellows thus produced have no joint welds, and, hence, the possibility of a loss of sealing, in this case, is somewhat lower. Also, the procedure of checking such bellows is much easier. However, the production procedure under consideration does not allow for any reduction in the percentage of defective products either. In particular, such deficiency as a loss of sealing occurs rather often. The frequency of local disintegrations and ruptures of the bellows wall is reduced slightly. The main cause of these deficiencies is non-uniformity of the grained structure of the alloy, arising from the heat treatment in the course of producing bellows. It will be understood that the non-uniformity of the structure of the alloy is responsible for anisotropy of its mechanical properties. This being the case, the bellows wall is sure to have portions of reduced strength. Under operating conditions, these portions are susceptible to cracking. Investigations prove that the size of some grains of the alloy are as high 60 to 80 .mu.m. A loss of sealing is sure to occur in the zone of such a grain when it is considered that the wall thickness of bellows may be as thin as 0.15 .mu.m and even 0.08 .mu.m. The non-unfiformity of the grained structure of the alloy is partly brought about by the non-uniformity of the temperature field in the muffle furnace. However, this is not the only cause.
It is also to be noted that the long residence time of the workpiece in the furnace (3 to 5 hours) is attended with an intensive formation of scale on the bellows wall. In addition, the oxidation processes propagate through the intergranular spaces and in the long run adversely affect the physical and mechanical properties of the alloy.
At the same time, the heat treatment which weakens the reeled tubular workpiece and the thermal stabilization of the corrugated workpiece are indispensible in this case. Otherwise the workpiece wall fails to be plastically deformed in the course of making corrugations and physical and mechanical properties of the alloy fail to meet the predetermined requirements.